The use of well bore signals for well logging and general communication of signals along the drill string bore is well established in an art usually referred to as Measurement While Drilling (MWD). It may be used with any pipe string in the well bore whether drilling or not and usually involves the same equipment and technique without changing the definition.
There are two general classifications of down hole pulsers, those installed in the drill string and those, called shuttle pulsers, transportable through the drill string bore to and from the down hole location. The installed version is assembled into the drill string at the surface while the down hole assembly is out of the well and can only be removed when the string is tripped. The shuttle pulser normally requires a housing that is part of the drill string and usually includes a shuttle locator and an orifice and that housing is installed while the down hole assembly is at the surface.
The pulser requires some form of power for operation. The down hole instrument requires power for instrument driving and signal processing. The pulser valve that creates the pressure pulse in the drilling fluid consumes a considerable amount of power. The installed pulser rarely operates on batteries alone and usually has a mud powered motor driving an electric generator of some form to power at least the instrument. In some cases the motor drives a hydraulic pump to provide signal valve operating power. All known shuttle pulsers operate on battery power alone. Powering the signal valve directly by batteries is not practical because batteries now available for the limited space in the shuttle would have a very short life.
The drilling fluid stream moving in the drill string bore has rather massive capability as a power source to drive the signal valve without significant drain upon the main purpose for the drilling fluid stream. Both forms of modern pulsers use the mud stream to derive power for the valve with only minimal power use from batteries for valve control. It is the derivation of power from the mud stream and the efficient utilization of electric power for valve control that this invention addresses.
It is therefore an object of this invention to provide apparatus to utilize the difference, in pressure drop across the signal valve, between the on-pulse and off-pulse states of the signal valve to provide the power to operate the signal valve.
It is another object of this invention to utilize the power derived from any change of state of the signal valve to power the next change of state of the signal valve.
It is yet another object to provide automatic locking means to secure the signal valve in each state until a signal for change of state is received from the controlling down hole instrument.
It is still a further object to provide means to regulate the pressure differential across the signal to a preselected amount.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.